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181
Encryption.cs
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181
Encryption.cs
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namespace GeoSus.Server;
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using System.Security.Cryptography;
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using System.Text;
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// Šifrování komunikace - RSA handshake + AES-256-CBC session (kompatibilní s Unity)
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public class ServerEncryption : IDisposable
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{
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private readonly RSA _rsa;
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private readonly string _publicKeyPem;
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public ServerEncryption(int keySizeBits = 2048)
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{
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_rsa = RSA.Create(keySizeBits);
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_publicKeyPem = ExportPublicKeyPem();
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}
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public string PublicKeyPem => _publicKeyPem;
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// Dešifruje session key od klienta
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public (byte[] Key, byte[] IV) DecryptSessionKey(string encryptedKeyBase64, string encryptedIvBase64)
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{
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var encryptedKey = Convert.FromBase64String(encryptedKeyBase64);
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var encryptedIv = Convert.FromBase64String(encryptedIvBase64);
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// Používáme OaepSHA1 pro Unity kompatibilitu
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var key = _rsa.Decrypt(encryptedKey, RSAEncryptionPadding.OaepSHA1);
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var iv = _rsa.Decrypt(encryptedIv, RSAEncryptionPadding.OaepSHA1);
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return (key, iv);
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}
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private string ExportPublicKeyPem()
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{
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var publicKey = _rsa.ExportSubjectPublicKeyInfo();
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var base64 = Convert.ToBase64String(publicKey);
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var sb = new StringBuilder();
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sb.AppendLine("-----BEGIN PUBLIC KEY-----");
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for (int i = 0; i < base64.Length; i += 64)
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{
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sb.AppendLine(base64.Substring(i, Math.Min(64, base64.Length - i)));
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}
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sb.AppendLine("-----END PUBLIC KEY-----");
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return sb.ToString();
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}
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public void Dispose()
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{
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_rsa.Dispose();
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}
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}
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// Session šifrování pro konkrétní klientské spojení - AES-256-CBC + HMAC-SHA256
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public class SessionCrypto : IDisposable
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{
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private readonly byte[] _key;
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private readonly object _lock = new();
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public SessionCrypto(byte[] key, byte[] iv)
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{
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if (key.Length != 32)
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throw new ArgumentException("Key musí být 32 bajtů pro AES-256");
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if (iv.Length != 16)
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throw new ArgumentException("IV musí být 16 bajtů pro AES-CBC");
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_key = key;
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// IV se nepoužívá přímo - každá zpráva má svůj unikátní IV
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}
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// Šifruje zprávu s AES-CBC a HMAC
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public byte[] Encrypt(byte[] plaintext)
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{
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lock (_lock)
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{
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using var aes = Aes.Create();
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aes.Key = _key;
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aes.Mode = CipherMode.CBC;
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aes.Padding = PaddingMode.PKCS7;
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aes.GenerateIV(); // Generujeme nový IV pro každou zprávu
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byte[] ciphertext;
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using (var encryptor = aes.CreateEncryptor())
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{
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ciphertext = encryptor.TransformFinalBlock(plaintext, 0, plaintext.Length);
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}
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// Počítáme HMAC přes IV + ciphertext (používáme AES klíč pro HMAC)
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byte[] hmac;
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using (var hmacSha = new HMACSHA256(_key))
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{
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var dataToSign = new byte[aes.IV.Length + ciphertext.Length];
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Buffer.BlockCopy(aes.IV, 0, dataToSign, 0, aes.IV.Length);
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Buffer.BlockCopy(ciphertext, 0, dataToSign, aes.IV.Length, ciphertext.Length);
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hmac = hmacSha.ComputeHash(dataToSign);
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}
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// Výstup: [16 bytes IV][32 bytes HMAC][ciphertext]
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var result = new byte[16 + 32 + ciphertext.Length];
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Buffer.BlockCopy(aes.IV, 0, result, 0, 16);
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Buffer.BlockCopy(hmac, 0, result, 16, 32);
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Buffer.BlockCopy(ciphertext, 0, result, 48, ciphertext.Length);
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return result;
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}
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}
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// Dešifruje zprávu a validuje HMAC
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public byte[]? Decrypt(byte[] encrypted)
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{
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if (encrypted.Length < 48) return null; // 16 IV + 32 HMAC + min data
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try
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{
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var iv = new byte[16];
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var receivedHmac = new byte[32];
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var ciphertext = new byte[encrypted.Length - 48];
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Buffer.BlockCopy(encrypted, 0, iv, 0, 16);
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Buffer.BlockCopy(encrypted, 16, receivedHmac, 0, 32);
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Buffer.BlockCopy(encrypted, 48, ciphertext, 0, ciphertext.Length);
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// Ověříme HMAC (používáme AES klíč pro HMAC)
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byte[] computedHmac;
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using (var hmacSha = new HMACSHA256(_key))
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{
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var dataToVerify = new byte[16 + ciphertext.Length];
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Buffer.BlockCopy(iv, 0, dataToVerify, 0, 16);
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Buffer.BlockCopy(ciphertext, 0, dataToVerify, 16, ciphertext.Length);
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computedHmac = hmacSha.ComputeHash(dataToVerify);
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}
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// Constant-time porovnání
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if (!CryptographicOperations.FixedTimeEquals(receivedHmac, computedHmac))
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{
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return null; // HMAC mismatch - zpráva byla změněna
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}
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// Dešifrujeme
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using var aes = Aes.Create();
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aes.Key = _key;
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aes.IV = iv;
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aes.Mode = CipherMode.CBC;
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aes.Padding = PaddingMode.PKCS7;
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using var decryptor = aes.CreateDecryptor();
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return decryptor.TransformFinalBlock(ciphertext, 0, ciphertext.Length);
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}
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catch (CryptographicException)
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{
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return null;
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}
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}
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public void Dispose()
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{
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Array.Clear(_key, 0, _key.Length);
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}
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}
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// Klientská strana - generuje session key a šifruje ho RSA public key
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public static class ClientEncryptionHelper
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{
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public static (byte[] Key, byte[] IV) GenerateSessionKey()
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{
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var key = RandomNumberGenerator.GetBytes(32); // AES-256
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var iv = RandomNumberGenerator.GetBytes(16); // AES-CBC IV (16 bytes)
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return (key, iv);
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}
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public static (string EncryptedKey, string EncryptedIV) EncryptSessionKey(
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string rsaPublicKeyPem, byte[] key, byte[] iv)
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{
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using var rsa = RSA.Create();
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rsa.ImportFromPem(rsaPublicKeyPem);
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var encryptedKey = rsa.Encrypt(key, RSAEncryptionPadding.OaepSHA256);
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var encryptedIv = rsa.Encrypt(iv, RSAEncryptionPadding.OaepSHA256);
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return (Convert.ToBase64String(encryptedKey), Convert.ToBase64String(encryptedIv));
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}
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}
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